Overview of the flare observations. (a-b) AIA 131 Å images of the flare at 13:12:32 UT and 13:56:32 UT, respectively. (c) Performances of a BSAD at different times in the region denoted by the box in panel (a). The ellipse indicates the body of the BSAD, and the dot-dashed curve in panel (c1) denotes the front of the BSAD. The dotted lines in panel (c7) mark the compressed plasma boundaries. The animation shows the sunward motion of BSADs. (The associated movie is available online.)